Own measured data

A multicomponent solar thermal system was installed in Bishkek to preheat water for a district heating net in the context of a joint research project of Kassel University (Germany) and Kyrgyz State Technical University in Bishkek (Kyrgyzstan). For detailed investigations different parameters including solar radiation are measured since autumn 2004 with very accurate sensors every 15 seconds to generate one-minute mean values. Solar radiation is measured with pyranometer Kipp&Zonen CM11 with an accuracy of 1.5% of the measured values. For some periods, however, the measurement data is missing for different reasons (e. g. technical problems with the sensor power supply unit or no power supply at all). For this study mean values of monthly solar irradiation were generated from the available measurement data for the period 2005 — 2007.

The focus of this study is to compare values of ambient temperature and solar irradiation from the mentioned sources because these two parameters are the most important for estimation of solar energy gains. The following abbreviations are applied for the sources of meteorological data:

• FrunzeM — measurements from weather station Frunze

• Met 5.1 and Met 6.0 — Meteonorm 5.1 and Meteonorm 6.0 respectively

• MD — own measurement data

A fluctuation of mean annual ambient temperatures measured by the local meteorological station Frunze since 1928 and long term mean ambient temperatures are shown in Fig. 2.

A long term mean temperature from both versions of Meteonorm is about 0.2 K higher than that measured by the station Frunze. The difference results from different periods considered. In Meteonorm a long-term mean ambient temperature is calculated for the period from 1961 till 1990 (30 years), while a mean temperature from the station Frunze is calculated for the period from 1928 till 2003 (75 years). For the same period 1961-1990, mean temperatures from the station Frunze and Meteonorm are in agreement (see Table 1).

A fluctuation of annual global solar irradiation and its mean values from different sources are shown in Fig. 3. The annual global solar irradiation from the station Frunze for the years 2003­2007 is estimated from 6 solar radiation measurements per day (see section 2.1).

Annual global solar irradiation from own measurements («1500 kWh/m2a) and the weather station Frunze (1572 kWh/m2a) are in a good agreement, while its values from Meteonorm 5.1 and 6.0 are approx. 20% lower (see Fig. 3) and even out of the fluctuation range.

FrunzeM /

зі

*

As shown in Fig. 4, the solar irradiation from Meteonorm and other sources are in a good agreement in winter. In the period March — September the monthly diffuse solar irradiation values generated with Meteonorm are higher than the measured values, which leads to lower global solar irradiation values. The higher values of diffuse solar irradiation in Meteonorm are probably caused

by admitting higher cloudiness or air pollution. Furthermore, the concavity in summer of the monthly global solar irradiation generated with Meteonorm 5.1 is not typical for a continental climate. It is also inconsistent with the monthly sunshine duration for Bishkek (see Fig. 5), which has no concavity or only one maximum point.

Fig. 4. Monthly global and diffuse solar irradiation for Bishkek from different sources.

If the latitude of Bishkek in Meteonorm 6.0 is changed from 42.8°N to 42.2°N, annual global irradiation increases to 1466 kWh/m2a (+20%) and annual diffuse irradiation decreases to

618 kWh/m2a (-7%). Thus, the radiation data for 42.2°N latitude is in the same range with the measurement data from the local weather station Frunze and the research project (MD). The same tendency occurs if the latitude of Bishkek is changed from 42.8°N to 43.4°N (1468 and 625 kWh/m2a or +20% and -6% respectively). This high change in the radiation data for a little change in the location is probably caused by the interpolation method of Meteonorm.

°C

13.5

13

12.5 12

11.5 11

10.5 10

9.5 9

As shown in Fig. 6, the annual global solar irradiation and the mean annual ambient temperature measured at the weather station Frunze in the period 1970 — 1991 are not positively correlated. The seasons (summer, autumn, winter, spring) and single months have the same tendency. The reason is that the weather and the ambient temperature in Kyrgyzstan are influenced not only by solar radiation but also by 17 weather processes [5], e. g. Siberian anticyclone brings cold air from Siberia.

Solar radiation and ambient temperature data from different sources (a local weather station, Meteonorm 5.1 and 6.0 and own measurements) have been compared with each other for Bishkek, Kyrgyzstan in this study. It was identified that the altitude of Bishkek city in Meteonorm is wrongly defined (2111 m instead of 760 m), which leads to significantly lower ambient temperatures. Therefore, it is necessary to define Bishkek manually as a new site with the correct coordinates. In this case the ambient temperatures are in agreement with those measured by the weather station Frunze.

Annual global solar irradiation from own measurements (1500 kWh/m2a) and weather station Frunze (1572 kWh/m2a) are in a good agreement, while its values from Meteonorm 5.1 and 6.0 are approx. 20% lower. Correspondingly, the ratio of the direct and diffuse solar irradiation is much lower in the Meteonorm data (approx. 1) than in the weather station Frunze data and own

measurement data (approx. 2). Furthermore, monthly sums of global solar irradiation generated with Meteonorm 5.1 have an untypical trend in summer, having two local maximum points. This is inconsistent with irradiation data from other sources and with the sunshine duration in the relevant period.

Such differences in solar radiation data can lead to significantly different solar gain predictions, especially if the solar irradiation on a tilted surface shall be calculated. Thus, the source of meteorological data shall be carefully selected. For sites, close to weather stations with relevant data available in the Meteonorm database, data generated with Meteonorm can be applied. If no weather station with relevant data close to the desired site available in Meteonorm database, other sources should be considered too, e. g. satellite-derived radiation rata, local meteorological stations or own measurements. In both cases, the data from Meteonorm should be proved on plausibility, particularly for sites or stations in developing countries.

The authors would like to express their gratitude to the Volkswagen Foundation, Germany for the financial support of the research project and the Central administrative board on hydrometeorology of Ministry of Emergency Measures of the Kyrgyz Republic for providing the meteorological data from the weather station “Frunze”.

Electric shower heads are presently installed in 73.1 % of the Brazilian houses. These devices accounts for around 60 % of the peak load in between 6:00 p. m. and 8:00 p. m., as is shown by reports of the Brazilian electric power system [1]. As demonstrated in a large scale experiment [2], Compact Solar Domestic Hot Water Systems (CSDHWS), conjugated to electric shower heads, are able to reduce the mentioned peak load due to shower heads by around 60 %. However the peak is expected to remain unchanged for those days of low solar radiation incidence. To further increase the peak power reduction and its confidence, an intelligent compact solar domestic hot water systems is under development and first simulation and optimization were carried out in [3] and [4]. According to the proposed system preheating by auxiliary energy should be done in order to provide preheated water at 6:00 a. m. and a specified storage water temperature at 6:00 p. m. Thus the preheating energy depends on daily available solar energy. Apart from the features solar energy use and peak reduction, additional advantage of this system is obtained by heating the water of the